1. Field of the Invention
The present invention generally relates to radiation sensors, and in particular, to compensating operating parameters and/or output signals of radiation sensors for changes in temperature of the sensors.
2. Discussion of the Related Art
A radiation detector is a device that produces an output signal which is a function of an amount of radiation that is incident upon an active region of the radiation detector. Radiation detectors may be designed and constructed to be sensitive to particular regions of the electromagnetic spectrum. For example, infrared detectors are radiation detectors that are sensitive to radiation in the infrared region of the electromagnetic spectrum. One example of an infrared detector includes a thermal detector, which detects radiation based upon a change in the temperature of an active region of the detector due to absorption of radiation incident to the detector.
A variety of imaging sensors may be constructed using an array of radiation detectors. Such sensors may be used in an imaging system that produces an image (e.g., on a display) based on radiation impinging on the imaging sensor. Based on the type of detectors used, the imaging sensor may be responsive to a particular region of spectrum. For example, an infrared or thermal imaging sensor may include a number of thermal detectors that detect a representation of an object by the objects"" thermal emissions. In particular, energy emitted by an object may depend on numerous quantities such as, for example, the emissitivity and the temperature of the object. Infrared thermal sensors typically detect one or both of these quantities and use the detected information to produce an object image that may be viewed, for example, on a display.
One issue in connection with at least some types of radiation detectors is that often it may be challenging to separate those signals output by the detector that are actually due to radiation of interest incident to the detector from various undesirable components which may be present in the detector output signals. For example, detector output signals may include various undesirable components due to variations in temperature of the detector itself that are not necessarily due to the radiation of interest.
In particular, temperature changes in the vicinity of the detector that may affect the temperature of the detector, sometimes referred to as ambient temperature variations (e.g., changes in temperature of a substrate on which the detector is fabricated, changes in temperature of a package in which the detector is housed, average temperature changes in a scene of interest itself), in turn may cause undesirable components to be present in the detector output signals. In some cases, these undesirable components may be hundreds of times larger than the instantaneous signals resulting from the radiation of interest, thereby detrimentally reducing the dynamic range of the detector and/or processing circuitry associated with the detector with respect to the radiation of interest.
In view of the foregoing, some conventional imaging systems employing imaging sensors comprising a number (e.g., array) of radiation detectors require some type of temperature stabilization of the detectors to reduce such undesirable components in the detector output signals. In particular, with respect to conventional thermal imaging systems, it is generally thought to be impractical to operate such systems without active stabilization of the temperature of the detectors. In some cases, thermal stabilization components may include a thermoelectric cooler (hereinafter, xe2x80x9cTE coolerxe2x80x9d) which is thermally coupled to the detectors (e.g., the substrate on which the detectors are fabricated is mounted on the TE cooler) to hold the detectors at a predetermined temperature. Depending on the difference between the predetermined stabilization temperature and the actual ambient temperature in the vicinity of the detectors, the TE cooler may consume appreciable power resources of the imaging system.
One embodiment of the invention is directed to a method of compensating a radiation sensor for changes in at least one operational characteristic of the sensor due to a temperature variation of the sensor. The method comprises an act of dynamically adjusting at least one operating parameter associated with the radiation sensor and/or at least one calibration parameter associated with the radiation sensor based on the temperature variation of the sensor.
According to one aspect of this embodiment, the at least one operational characteristic of the sensor that changes due to the temperature variation of the sensor includes a resistance of the sensor.
According to another aspect of this embodiment, the at least one operating parameter associated with the sensor includes at least one of a DC bias voltage applied to the sensor, a DC bias current applied to the sensor, and an AC bias waveform applied to the sensor.
According to another aspect of this embodiment, the sensor includes a plurality of radiation detectors, and the at least one calibration parameter associated with the sensor includes at least one of an offset error value for each radiation detector and a gain value for each radiation detector.
According to another aspect of this embodiment, the sensor includes a plurality of radiation detectors, and the at least one operational characteristic of the sensor that changes due to the temperature variation of the sensor includes at least one of an offset error variation and a gain variation.
Another embodiment of the invention is directed to an apparatus, comprising a controller to compensate a radiation sensor for changes in at least one operational characteristic of the sensor due to a temperature variation of the sensor. The controller dynamically adjusts at least one operating parameter associated with the radiation sensor and/or at least one calibration parameter associated with the radiation sensor based on the temperature variation of the sensor.